A process of production of acrylic acid or methacrylic acid through dehydration-condensation of acetic acid or propionic acid and formaldehyde is well known in the art, and the following have been proposed as useful catalysts.
Examples of catalysts include a basic catalyst such as a catalyst comprising an alkali or alkaline earth metal hydroxide carried on alumina silicate or silica gel (Japanese Patent Publication No. 21928/70), a basic catalyst comprising calcined silica (Japanese Patent Application (OPI) No. 70919/74 (the term "OPI" as used herein means a "published unexamined Japanese patent application")), a basic catalyst having a great surface area (Japanese Patent Publication No. 40130/82), a catalyst comprising an alkali metal carboxylate carried on active alumina (U.S. Pat. No. 3,051,747), a catalyst comprising a metaphosphoric acid alkali metal or alkaline earth metal salt carried on silica gel (Japanese Patent Publication No. 16728/71), and an aluminosilicate catalyst containing an alkali metal or alkaline earth metal salt (U.S. Pat. No. 3,247,248), a phosphate-based catalyst (Japanese Patent Application (OPI) No. 123137/82), a vanadium-antimony catalyst (Japanese Patent Application (OPI) No. 123138/82), a vanadium orthophosphate catalyst (U.S. Pat. No. 4,165,438), etc.
Most of the known catalysts are basic catalysts or catalysts containing a basic component. The reason for this is that the dehydration-condensation reaction of acetic acid or propionic acid with formaldehyde is believed to proceed following a similar mechanism to that of the Claisen condensation occurring in the presence of a strong base.